JP2002040505A - Quantum circuit - Google Patents
Quantum circuitInfo
- Publication number
- JP2002040505A JP2002040505A JP2000230366A JP2000230366A JP2002040505A JP 2002040505 A JP2002040505 A JP 2002040505A JP 2000230366 A JP2000230366 A JP 2000230366A JP 2000230366 A JP2000230366 A JP 2000230366A JP 2002040505 A JP2002040505 A JP 2002040505A
- Authority
- JP
- Japan
- Prior art keywords
- state
- photon absorption
- photon
- crystal
- incident
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/70—Photonic quantum communication
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
- H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
- H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
- H04L9/0852—Quantum cryptography
- H04L9/0858—Details about key distillation or coding, e.g. reconciliation, error correction, privacy amplification, polarisation coding or phase coding
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Optics & Photonics (AREA)
- Theoretical Computer Science (AREA)
- Computer Security & Cryptography (AREA)
- Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
- Light Receiving Elements (AREA)
- Optical Communication System (AREA)
- Photometry And Measurement Of Optical Pulse Characteristics (AREA)
Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は光を用いた量子通信
・量子計算機に関し、特に量子状態測定を行う量子回路
に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quantum communication / quantum computer using light, and more particularly to a quantum circuit for measuring a quantum state.
【０００２】[0002]
【従来の技術】インターネットの爆発的普及、電子商取
引の実用化を迎え、通信の秘密保持・改竄防止や個人の
認証など暗号技術の社会的な必要性が高まっている。現
在、ＤＥＳ暗号のような共通鍵方式やＲＡＳ暗号をはじ
めとする公開鍵方式が広く用いられている。しかし、こ
れらは「計算量的安全性」にその基盤を置いている。つ
まり、現行の暗号方式は計算機ハードウェアと暗号解読
アルゴリズムの進歩に常に脅かされている。これに対し
て、量子暗号のような「物理暗号」は物理法則が暗号の
安全性を保証するため、計算機の能力の限界に依存しな
い究極の安全性保証が可能になる。このような暗号方式
が実用になればその社会的インパクトは極めて大きく、
将来の情報産業における技術的基盤の一つとなることが
期待できる。2. Description of the Related Art With the explosive spread of the Internet and the practical use of electronic commerce, there is a growing social need for cryptographic techniques such as confidentiality and prevention of falsification of communications and personal authentication. At present, public key systems such as a common key system such as the DES encryption and RAS encryption are widely used. However, they are based on "computational security". In short, current cryptography is constantly threatened by advances in computer hardware and decryption algorithms. In contrast, “physical cryptography” such as quantum cryptography guarantees the security of cryptography according to the physical laws, and thus enables ultimate security assurance that does not depend on the limit of computer capability. If such an encryption method becomes practical, its social impact will be extremely large,
It can be expected to be one of the technological bases in the future information industry.
【０００３】量子暗号をはじめとする量子情報は伝送に
用いる量子（光子）の損失や擾乱により距離が数十ｋｍ
に制限される。また、通信の相手も伝送線である光ファ
イバの両端に限られ、量子通信を多くの相手と行う場合
には光ファイバを数多く引く必要がある。このような問
題点を解消し、量子情報通信を広い範囲にわたって行う
量子ネットワーキングを実現するためには中継や交換と
いった技術が必要になる。もちろん量子情報を中継局で
古典情報に直せば中継や交換を行うことができるが、量
子情報通信の特質がここで途切れてしまう。例えば、量
子暗号鍵配布を行う場合、中継局に侵入されれば全ての
情報は盗聴可能になってしまい、量子情報の利点である
盗聴に対する安全性が損なわれる。[0003] Quantum information such as quantum cryptography has a distance of several tens of km due to loss or disturbance of quantum (photons) used for transmission.
Is limited to Also, the communication partner is limited to both ends of the optical fiber which is a transmission line, and when performing quantum communication with many partners, it is necessary to draw many optical fibers. In order to solve such problems and realize quantum networking for performing quantum information communication over a wide range, techniques such as relaying and switching are required. Of course, if the quantum information is converted into classical information at a relay station, relaying and exchange can be performed, but the characteristics of quantum information communication are interrupted here. For example, when quantum cryptographic key distribution is performed, if information is entered into a relay station, all information can be eavesdropped, and the security against eavesdropping, which is an advantage of quantum information, is impaired.
【０００４】そこで、量子情報をそのまま中継・交換す
る量子中継・量子交換が必要になる。量子中継・量子交
換は分散型の量子コンピュータにとっても重要である。
量子中継は量子テレポーテーションを用いると以下のよ
うに実現できる。量子情報は量子相関を担うもつれ合っ
た光子対と古典情報に分けて運ばれる。エンタングルメ
ントスワッピングを利用するともつれ合った光子対を次
々に乗り換えていくことができる。これによって遠くは
なれた場所でも、もつれ合った光子対を共有できる。量
子テレポーテーションやエンタングルメントスワッピン
グにはもつれ合った光子対の生成とベル状態測定が必須
である。ベル状態測定とは２つの光子がベル状態と呼ば
れる４つのもつれ合った状態のいずれに属するかを決定
するものである。量子テレポーテーションやエンタング
メルントスワッピングの原理は実験でも確かめられてい
る。しかし、現在ある技術では４つ全てのベル状態を判
別することはできない。そのため、任意の量子状態の伝
送は実現できていない。Therefore, quantum relay / quantum exchange for relaying / exchanging quantum information as it is becomes necessary. Quantum relay / quantum exchange is also important for distributed quantum computers.
Quantum relay can be realized as follows using quantum teleportation. Quantum information is transported separately into entangled photon pairs that carry the quantum correlation and classical information. The use of entanglement swapping makes it possible to switch entangled photon pairs one after another. This allows entangled photon pairs to be shared even in remote locations. For quantum teleportation and entanglement swapping, generation of entangled photon pairs and Bell state measurement are essential. Bell state measurement determines which of the four entangled states the two photons belong to, called the bell state. The principles of quantum teleportation and entanglement swapping have been confirmed in experiments. However, existing technologies cannot distinguish all four bell states. Therefore, transmission of an arbitrary quantum state has not been realized.
【０００５】古沢（Ｆｕｒｕｓａｗａ，Ａ．）らはサイ
エンス（Ｓｃｉｅｎｃｅ）誌２８２巻７０６ページ（１
９９８年）においてベル状態測定を必要としない量子テ
レポーテーションを報告した。この方法では任意の量子
状態の伝送が可能だが１００％スクイージングした光を
必要とする。現在得られている光源のスクイージングが
十分でないため伝送された量子状態の忠実度は５８％と
低い値しか得られていない。一方、ベル状態測定が実現
できればほぼ１００％の忠実度が期待できる。Furusawa, A. et al., Science, vol. 282, page 706 (1)
998) reported quantum teleportation that does not require bell state measurements. This method allows transmission of any quantum state, but requires 100% squeezed light. Since the squeezing of the currently obtained light source is not sufficient, the fidelity of the transmitted quantum state is as low as 58%. On the other hand, if bell state measurement can be realized, almost 100% fidelity can be expected.
【０００６】この目的のために、通常、半透鏡と偏光ビ
ームスプリッタといった線形光学素子と光子検出器から
なる検出回路を用いた手法が採用されている。しかしな
がら、この手法では４つのベル状態のうち、２つの状態
しか判別できない。２光子のベル状態をｘ軸方向に偏光
した光子｜ｘ＞とｙ軸方向に偏光した光子｜ｙ＞で表す
と Φ（±）＝（｜ｘ＞｜ｘ＞±｜ｙ＞｜ｙ＞）／√２ Ψ（±）＝（｜ｘ＞｜ｙ＞±｜ｙ＞｜ｘ＞）／√２ のようにかける。ベル状態はある偏光の組に属する２光
子状態と２光子の偏光を入れ替えた状態の重ね合わせ状
態になっている。Φ（±）は２光子が同じ方向の偏光を
持ち、偏光方向の交換に対して対称（＋）または反対称
（−）な状態、Ψ（±）は２光子が異なる方向の偏光を
持ち、偏光方向の交換に対して対称（＋）または反対称
（−）な状態である。図５に示した半透鏡５１と偏光ビ
ームスプリッタ５２，５３からなる線形光学素子による
ベル状態測定回路に４つのベル状態のどれかを入射す
る。光子検出器５４〜５７の応答から可能なベル状態を
求めると表１のようになる。これから、図５に示した線
形光学素子によるベル状態測定回路はΨ（±）状態は判
別できるが、Φ（±）状態のどちらかは判別できないこ
とが分かる。光制御ＮＯＴゲートとよばれる量子ゲート
を用いれば４つ全てのベル状態を判別できることが知ら
れているがこのような量子ゲートで実現可能なものはま
だ知られていない。For this purpose, a method using a detection circuit comprising a linear optical element such as a semi-transparent mirror and a polarizing beam splitter and a photon detector is usually employed. However, with this method, only two of the four bell states can be determined. When the bell state of two photons is represented by a photon polarized in the x-axis direction | x> and a photon polarized in the y-axis direction | y>, Φ (±) = (| x> | x> ± | y> | y>) / √2√ (±) = (| x> | y> ± | y> | x>) / √2 The bell state is a superimposed state of a two-photon state belonging to a certain set of polarizations and a state in which the polarizations of the two-photons are exchanged. Φ (±) indicates that two photons have polarization in the same direction and is symmetric (+) or antisymmetric (−) with respect to the exchange of polarization direction, Ψ (±) indicates that two photons have polarization in different directions, It is symmetric (+) or anti-symmetric (-) with respect to the exchange of the polarization direction. One of the four bell states is incident on a bell state measuring circuit composed of a linear optical element including the semi-transparent mirror 51 and the polarization beam splitters 52 and 53 shown in FIG. Table 1 shows the possible bell states obtained from the responses of the photon detectors 54 to 57. From this, it can be seen that the bell state measuring circuit using the linear optical element shown in FIG. 5 can discriminate the Ψ (±) state but cannot discriminate between the Φ (±) state. It is known that all four Bell states can be determined by using a quantum gate called an optically controlled NOT gate, but what can be realized with such a quantum gate is not yet known.
【０００７】[0007]
【表１】 最近、スカリー（Ｓｃｕｌｌｙ， Ｍ．Ｏ．）らはフィ
ジカルレビューレターズ（Ｐｈｙｓｉｃａｌ Ｒｅｖｉ
ｅｗ Ｌｅｔｔｅｒｓ）誌８３巻４４３３頁（１９９９
年）において２光子吸収を利用したベル状態測定の方法
を提案している。この方法では円偏光でベル状態を表
し、２光子吸収を行う３つの原子セルを通し、原子セル
からの２光子吸収に伴う蛍光を観測する。セル内の原子
をあらかじめ強い電磁場によって波動関数が特別の重ね
合わせ状態になるように準備しておくと特定のベル状態
だけを吸収するようにできるからどのセルで吸収された
かを観測することでどのベル状態の光が入射したか判断
できる。３つのセルがいずれも２光子吸収しなかったと
きは残りの一つのベル状態が入射したと結論する。[Table 1] Recently, Scully, MO et al., Physical Review Letters.
ew Letters), 83, 4433 (1999)
(Year) proposed a method for measuring the Bell state using two-photon absorption. In this method, the bell state is represented by circularly polarized light, and the fluorescence accompanying two-photon absorption from the atomic cell is observed through three atomic cells that perform two-photon absorption. If the atoms in the cell are prepared in advance so that the wave function is in a special superimposed state by a strong electromagnetic field, it is possible to absorb only a specific Bell state, so by observing which cell absorbed it, It can be determined whether the light in the bell state has entered. When none of the three cells absorbed two photons, it concluded that the remaining one bell state was incident.
【０００８】[0008]
【発明が解決しようとする課題】しかしながら、スカリ
ーらの方法はあらかじめ強い電磁場によって波動関数が
特別の重ね合わせ状態になるように準備された原子を２
光子吸収に用いている。原子を重ね合わせ状態に準備し
たまま保つことは容易ではない。しかも、彼らの方法で
はそのように準備された原子の入ったセルを３個必要と
する。また、原子は気体としてセル内にあるので密度が
小さく２光子吸収の確率が小さく、２光子吸収を十分高
い確率で得るためには極めて長いセルを必要とし実際的
でない。さらに、２光子吸収で励起された電子からの蛍
光を観測する確率もそれほど大きくはないので、蛍光が
観測できなかったとき、ベル状態の判別を誤る可能性が
高い。ベル状態の判別を誤ると忠実度の高い量子状態の
伝送はできない。However, according to the method of Scully et al., Two atoms prepared beforehand by a strong electromagnetic field so that the wave function is brought into a special superposition state.
Used for photon absorption. It is not easy to keep atoms ready for superposition. Moreover, their method requires three cells containing such prepared atoms. In addition, since atoms are present in the cell as a gas, their density is small, the probability of two-photon absorption is small, and a very long cell is required to obtain two-photon absorption with a sufficiently high probability, which is not practical. Furthermore, since the probability of observing fluorescence from electrons excited by two-photon absorption is not so large, when fluorescence cannot be observed, there is a high possibility of misjudgment of the Bell state. If the Bell state is erroneously determined, it is impossible to transmit a quantum state with high fidelity.
【０００９】本発明の主な目的は忠実度の高い量子状態
の伝送を実現するため、十分高い確率で２光子吸収し、
他の電磁場による原子状態の準備が不要な材料を用いて
ベル状態測定ができる実用的な量子回路を提供すること
である。A main object of the present invention is to realize two-photon absorption with a sufficiently high probability in order to realize transmission of a quantum state with high fidelity.
An object of the present invention is to provide a practical quantum circuit capable of performing Bell state measurement using a material that does not require preparation of an atomic state by another electromagnetic field.
【００１０】[0010]
【課題を解決するための手段】本発明による量子回路
は、結晶の対称性により特定の偏光方向をもつ２光子の
組を吸収する２光子吸収結晶と２光子吸収結晶における
２光子吸収を検出する手段と偏光の状態を変換する偏光
要素を備えることを特徴としている。この２光子吸収結
晶は量子干渉により特定のベル状態の光だけを２光子吸
収をする。２光子吸収で励起された電子は別に設けた検
出手段により検出される。偏光要素を用いるとベル状態
を別のベル状態に１対１で変換できる。２光子吸収結晶
を透過した光の状態を偏光要素によって別のベル状態に
変換して新たな２光子吸収結晶に入射して検出すること
を順次繰り返すことによって、ベル状態を全て判別でき
る。A quantum circuit according to the present invention detects a two-photon absorption crystal that absorbs a set of two-photons having a specific polarization direction due to the symmetry of the crystal, and detects two-photon absorption in the two-photon absorption crystal. And a polarizing element for changing a state of polarized light. This two-photon absorption crystal absorbs only the light in a specific bell state by two-photon absorption due to quantum interference. Electrons excited by two-photon absorption are detected by a separately provided detecting means. The use of a polarizing element allows one-to-one conversion of a bell state to another bell state. The Bell state can be completely discriminated by sequentially repeating the process of converting the state of the light transmitted through the two-photon absorption crystal into another Bell state using a polarizing element, and entering and detecting a new two-photon absorption crystal.
【００１１】また、前述の量子回路ではベル状態の判別
に４つの２光子吸収結晶を必要とするが、線形光学素子
を用いても２つの状態は判別できることから、線形光学
素子では判別できないΦ（＋）状態及び／又はΦ（−）
状態を２光子吸収結晶で吸収検出し、残りのΨ（＋）と
Ψ（−）を線形光学素子で判別することもできる。この
ような回路は以下のような構成になる。入射光の光路に
第１の偏光要素を挿入して、Φ（＋）あるいはΦ（−）
状態のいずれかを前記の特定のベル状態に変換してから
第１の２光子吸収結晶に入射する。２光子吸収で励起さ
れた電子は別に設けた検出手段により検出される。これ
によってΦ（＋）またはΦ（−）状態が検出される。さ
らに前記の２光子吸収結晶で吸収されなかった光に第２
の偏光要素を作用させ、第２の２光子吸収結晶に入射す
る。この第２の偏光要素は、第１の変換後に第１の２光
子吸収結晶で吸収されなかったΦ（＋）状態又はΦ
（−）状態であって第１の偏光要素で第１の変換をされ
た状態を第２の２光子吸収結晶が２光子吸収する特定の
ベル状態に更に変換する。これにより、残りのΦ（＋）
またはΦ（−）状態が検出される。２つの結晶で吸収さ
れなかった光はもともとΨ（±）状態にあったはずなの
で、さらに第３の偏光要素を用いて元のΨ（±）状態に
変換する。このベル状態を線形光学素子による回路で検
出する。以上の操作によって全てのベル状態を判別す
る。なお、第１と第２の２光子吸収結晶が検出する特定
のベル状態は同じ状態でも、異なる状態であってもよ
い。また、偏光要素による変換では、あるベル状態は別
のベル状態に変換され、異なるベル状態が同じベル状態
に変換されることはないので別のベル状態を誤って検出
することはない。また、２光子吸収結晶が検出する特定
のベル状態がΦ（＋）またはΦ（−）状態であるときは
第１の偏光要素と第３の偏光要素は不要である。第１と
第２の２光子吸収結晶がそれぞれΦ（＋）状態とΦ
（−）状態を検出するときは第２の偏光要素も不要にな
る。In the quantum circuit described above, four two-photon absorption crystals are required for discriminating the Bell state. However, since two states can be discriminated using a linear optical element, Φ ( +) State and / or Φ (-)
The state can be detected by absorption with a two-photon absorption crystal, and the remaining Ψ (+) and Ψ (-) can be discriminated by a linear optical element. Such a circuit has the following configuration. The first polarization element is inserted into the optical path of the incident light, and Φ (+) or Φ (−)
One of the states is converted to the above-mentioned specific bell state and then enters the first two-photon absorption crystal. Electrons excited by two-photon absorption are detected by a separately provided detecting means. As a result, the Φ (+) or Φ (-) state is detected. Further, the light not absorbed by the two-photon absorption crystal
And the light is incident on the second two-photon absorption crystal. This second polarizing element is in a Φ (+) state or Φ that has not been absorbed by the first two-photon absorbing crystal after the first conversion.
The (−) state, in which the first conversion is performed by the first polarizing element, is further converted to a specific bell state in which the second two-photon absorption crystal absorbs two photons. Thus, the remaining Φ (+)
Alternatively, a Φ (-) state is detected. Since the light not absorbed by the two crystals should have originally been in the Ψ (±) state, it is further converted to the original Ψ (±) state by using the third polarizing element. This bell state is detected by a circuit using a linear optical element. Through the above operation, all the bell states are determined. The specific bell state detected by the first and second two-photon absorption crystals may be the same state or different states. In the conversion by the polarization element, one bell state is converted to another bell state, and a different bell state is not converted to the same bell state, so that another bell state is not erroneously detected. When the specific Bell state detected by the two-photon absorption crystal is a Φ (+) or Φ (−) state, the first polarization element and the third polarization element are unnecessary. The first and second two-photon absorption crystals have a Φ (+) state and a Φ
When detecting the (-) state, the second polarizing element is not required.
【００１２】さらに、本発明によれば、４つのベル状態
がそれぞれ別の検出手段によって検出されるため、検出
に失敗した場合でも誤ったベル状態を検出する可能性は
検出器の雑音に起因するものだけなので小さい。このた
め、誤りの少ないベル状態の検出が実現できる。Further, according to the present invention, the four bell states are detected by different detecting means, respectively. Therefore, even if the detection fails, the possibility of detecting an erroneous bell state is caused by detector noise. It is small because it is only things. For this reason, detection of a bell state with few errors can be realized.
【００１３】このように、本発明は結晶の対称性に起因
する２光子吸収の偏光選択則と量子干渉による特定のベ
ル状態の検出と、偏光要素によるベル状態の変換によっ
て全てのベル状態の検出を行っており、あらかじめ原子
の波動関数を特別の重ね合わせ状態になるように準備す
る必要はない。また、固体を用いているため強い２光子
吸収が期待できる。従って、十分高い確率で２光子吸収
し、他の電磁場による原子状態の準備が不要な材料を用
いてベル状態測定ができる実用的な量子回路という効果
が得られる。As described above, according to the present invention, a specific bell state is detected by the polarization selection rule of two-photon absorption and quantum interference caused by the symmetry of a crystal, and all bell states are detected by converting the bell state by a polarization element. It is not necessary to prepare the wave functions of atoms in a special superimposed state in advance. In addition, strong two-photon absorption can be expected because a solid is used. Therefore, an effect of a practical quantum circuit capable of measuring the Bell state using a material that absorbs two-photons with a sufficiently high probability and does not need to prepare an atomic state by another electromagnetic field is obtained.
【００１４】通常、固体を用いた量子回路では位相緩和
が極めて速いことが問題になるが、本発明では２光子吸
収で励起された電子が可干渉性を保つ必要がないため、
位相緩和の影響を受けない。Usually, in a quantum circuit using a solid, the problem is that phase relaxation is extremely fast. However, in the present invention, it is not necessary for electrons excited by two-photon absorption to maintain coherence.
Not affected by phase relaxation.
【００１５】[0015]
【発明の実施の形態】本発明の上記および他の目的、特
徴および利点を明確にすべく、添付した図面を参照しな
がら、本発明の実施の形態を以下に詳述する。BRIEF DESCRIPTION OF THE DRAWINGS In order to clarify the above and other objects, features and advantages of the present invention, embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
【００１６】図１を参照すると、本発明の一実施形態と
しての量子回路の構成図が示されている。ここで用いる
２光子吸収結晶はＣｕＣｌのような立方晶で、入射する
光は励起子分子への２光子吸収に共鳴しているものとす
る。また、光は結晶面にほぼ垂直に入射するものとす
る。第１の２光子吸収結晶１１にベル状態を入射する。
第１の２光子吸収結晶１１を透過した光はｘおよびｙ方
向を主軸として二つの主軸方向の振動に９０度の位相差
を与える減速子１３、１４を通る。さらに、同種の結晶
からなる第２の２光子吸収結晶１２に入射する。第２の
２光子吸収結晶１２を透過した光を線形光学素子による
ベル状態測定回路１５で光子の状態を検出する。２光子
吸収で励起された励起子分子はそれぞれイオン化され、
光伝導信号として光伝導検出器１６、１７で検出され
る。Referring to FIG. 1, there is shown a block diagram of a quantum circuit according to an embodiment of the present invention. It is assumed that the two-photon absorption crystal used here is a cubic crystal such as CuCl, and that the incident light resonates with the two-photon absorption in the exciton molecule. It is assumed that light is incident on the crystal plane almost perpendicularly. The bell state is incident on the first two-photon absorption crystal 11.
The light transmitted through the first two-photon absorption crystal 11 passes through decelerators 13 and 14 that give a phase difference of 90 degrees to the vibrations in the two principal axes with the principal axes in the x and y directions. Further, the light is incident on a second two-photon absorption crystal 12 made of the same kind of crystal. The light transmitted through the second two-photon absorption crystal 12 is used to detect the state of a photon by a bell state measuring circuit 15 using a linear optical element. Exciton molecules excited by two-photon absorption are each ionized,
It is detected by the photoconductive detectors 16 and 17 as a photoconductive signal.
【００１７】ＣｕＣｌのような立方晶の励起子分子は全
対称状態（Γ１）にあるから、二つの直線偏光が入射し
たとき、偏光の向きが同じ時２光子吸収が起きる。つま
り、光は｜ｘ｜ｘか｜ｙ｜ｙの状態でなければならな
い。ベル状態のうち偏光の向きが異なるΨ（±）状態は
２光子吸収されない。Φ（＋）状態が入射すると｜ｘ｜
ｘと｜ｙ｜ｙからの吸収は強めあうが、Φ（−）状態が
入射すると｜ｘ｜ｘと｜ｙ｜ｙからの吸収は打ち消しあ
う。つまり本実施形態で用いる結晶の励起子分子への２
光子吸収ではΦ（＋）状態だけが検出される。第１の２
光子吸収結晶１１を透過した光は減速子１３、１４によ
って、Φ（−）状態はΦ（＋）状態に変換され、Ψ
（±）状態は変換されない。この状態を同種の結晶から
なる第２の２光子吸収結晶１２に入射するとΦ（＋）状
態に変換されたΦ（−）状態が２光子吸収を受ける。第
２の２光子吸収結晶１２でも吸収されなかった光はΨ
（±）状態にあるので線形光学素子によるベル状態測定
回路１５で判別される。以上４つのベル状態の全てが検
出される。Since cubic exciton molecules such as CuCl are in a state of total symmetry (Γ1), when two linearly polarized lights are incident, two-photon absorption occurs when the polarization directions are the same. That is, the light must be in the state of | x | x or | y | y. In the Bell state, the が (±) state in which the polarization directions are different does not absorb two photons. When the Φ (+) state enters, | x |
Although the absorption from x and | y | y increases, the absorption from | x | x and | y | y cancels out when the Φ (-) state enters. In other words, the crystal used in the present embodiment has 2
In the photon absorption, only the Φ (+) state is detected. First two
The light transmitted through the photon absorption crystal 11 is converted from the Φ (-) state to the Φ (+) state by the moderators 13 and 14, and Ψ
The (±) state is not converted. When this state enters the second two-photon absorption crystal 12 made of the same kind of crystal, the Φ (-) state converted to the Φ (+) state undergoes two-photon absorption. The light not absorbed by the second two-photon absorption crystal 12 is Ψ
Since it is in the (±) state, it is determined by the bell state measuring circuit 15 using the linear optical element. All of the four bell states are detected.
【００１８】立方対称の結晶で２光子吸収の終状態とし
て可能な状態は全対称状態（Γ１）の他にΓ３対称性を
持つものとΓ５対称性を持つものがある。これらの状態
はＣｕＢｒのように最高の価電子帯の対称性がΓ８であ
る結晶の励起子分子の励起状態である。また、励起子は
Γ５の対称性を持つ。２光子吸収の偏光選択則は表２に
示したクレプシュ・ゴルダン係数から求められる。In a cubic symmetric crystal, possible states as a final state of two-photon absorption include a state having Γ3 symmetry and a state having Γ5 symmetry in addition to the all symmetric state (Γ1). These states are excited states of the exciton molecules of a crystal such as CuBr having the highest valence band symmetry of Γ8. In addition, excitons have Γ5 symmetry. The polarization selection rule for two-photon absorption is obtained from the Klepsch-Gordan coefficient shown in Table 2.
【００１９】[0019]
【表２】 表２で０でない係数に対応した偏光の組み合わせのみが
２光子吸収される。係数の符号が等しければベル状態の
うち偏光方向の交換に対して対称な状態が、係数の符号
が逆のときは偏光方向の交換に対して反対称な状態が２
光子吸収される。[Table 2] Only the combination of polarizations corresponding to the non-zero coefficients in Table 2 is two-photon absorbed. If the signs of the coefficients are equal, two states of the Bell state that are symmetric with respect to the exchange of the polarization direction are opposite. If the signs of the coefficients are opposite, two states that are antisymmetric with respect to the exchange of the polarization direction are two.
Photon absorption.
【００２０】Γ３対称性を持つ状態を２光子吸収の終状
態とする結晶を用いると、偏光要素が不要になる。この
ときの量子回路の構成図を図２に示す。このときの結晶
は量子井戸とするか、１軸性の応力を印加するなどの手
段でΓ３対称性を持つ状態を二つに分裂させる。さらに
電界を印加するなどして、二つの状態のどちらか一方だ
けを入射光に２光子共鳴するように設定する。表２か
ら、Γ３対称性を持つ状態の一つはΦ（＋）状態を２光
子吸収し、もう一つはΦ（−）状態を２光子吸収する。
これら二つの状態は等しいエネルギーを持つが、量子井
戸のような正方対称な摂動場によってエネルギー的に分
離することができる。二つの状態のどちらか一方だけを
入射光に２光子共鳴するように設定した結晶を二つ用い
ることによってΦ（＋）状態とΦ（−）状態だけをそれ
ぞれ２光子吸収することができる。When a crystal having a state having three symmetry as a final state of two-photon absorption is used, a polarizing element becomes unnecessary. FIG. 2 shows a configuration diagram of the quantum circuit at this time. At this time, the crystal is split into two states having Γ3 symmetry by using a quantum well or by applying a uniaxial stress. Further, by applying an electric field or the like, only one of the two states is set so that two-photon resonance occurs with the incident light. From Table 2, one of the states having Γ3 symmetry absorbs the Φ (+) state by two photons, and the other state absorbs the Φ (−) state by two photons.
These two states have equal energies but can be separated energetically by a square symmetric perturbation field such as a quantum well. By using two crystals in which only one of the two states is set to resonate with the incident light in two photons, only the Φ (+) state and the Φ (−) state can be respectively absorbed by two photons.
【００２１】Γ５対称性を持つ状態を２光子吸収の終状
態とする結晶を用いるときの量子回路の構成図を図３に
示す。第１の２光子吸収結晶１１に入射する前の一方の
光路に偏光を９０度回転する偏光素子である旋回子３１
を挿入する。第１の２光子吸収結晶１１を透過した光の
一つはｘおよびｙ方向を主軸として二つの主軸方向の振
動に９０度の位相差を与える減速子１３を通り、もう一
つはｘおよびｙ方向を主軸として二つの主軸方向の振動
に−９０度の位相差を与える減速子１４を通る。第１の
２光子吸収結晶と同種の第２の２光子吸収結晶１２を透
過した光の光路の一つに偏光を−９０度回転する旋回子
３２を挿入する。このあと、線形光学素子からなる線形
光学素子であるベル状態測定回路回路１５で光子の状態
を検出する。FIG. 3 shows a configuration diagram of a quantum circuit using a crystal in which a state having Γ5 symmetry is a final state of two-photon absorption. A rotator 31 which is a polarizing element for rotating polarized light by 90 degrees in one optical path before entering the first two-photon absorption crystal 11
Insert One of the lights transmitted through the first two-photon absorption crystal 11 passes through a moderator 13 that gives a 90-degree phase difference to the vibrations in the two principal axes with the principal axes in the x and y directions, and the other one in x and y. It passes through a speed reducer 14 that gives a phase difference of -90 degrees to the vibrations in the two main axis directions with the direction as the main axis. A rotator 32 for rotating the polarization by -90 degrees is inserted into one of the optical paths of the light transmitted through the second two-photon absorption crystal 12 of the same kind as the first two-photon absorption crystal. Thereafter, the state of the photon is detected by a bell state measuring circuit 15 which is a linear optical element composed of a linear optical element.
【００２２】Γ５対称性を持つ状態を２光子吸収の終状
態とするとき、Ψ（＋）状態だけが２光子吸収を受け
る。旋回子はベル状態のうち、Φ（＋）状態をΨ（＋）
状態に変換する。このとき、Φ（−）状態はΨ（−）状
態に、Ψ（±）状態はΦ（±）状態にそれぞれ変換され
る。この状態の光を第１の２光子吸収結晶１１に入射す
るとΨ（＋）状態に変換されたΦ（＋）状態だけが２光
子吸収される。減速子によって、Ψ（−）状態はΨ
（＋）状態に変換されるが、Φ（±）状態は変換されな
い。第２の２光子吸収結晶１２ではもとのΦ（−）状態
だけが２光子吸収される。さらに、旋回子で透過したΦ
（±）状態に変換されていた光の状態が減速子３２で元
のΨ（±）状態に戻る。この状態を線形光学素子による
ベル状態測定回路１５で判別する。When the state having Γ5 symmetry is the final state of two-photon absorption, only the Ψ (+) state receives two-photon absorption. The swirler changes the Φ (+) state to Ψ (+) in the bell state.
Convert to state. At this time, the Φ (-) state is converted to a Ψ (-) state, and the Ψ (±) state is converted to a Φ (±) state. When the light in this state enters the first two-photon absorption crystal 11, only the Φ (+) state converted into the Ψ (+) state is two-photon absorbed. Due to the reducer, the Ψ (-) state changes to Ψ
It is converted to the (+) state, but not the Φ (±) state. In the second two-photon absorption crystal 12, only the original Φ (-) state is two-photon absorbed. In addition, Φ
The state of the light that has been converted to the (±) state returns to the original Ψ (±) state at the speed reducer 32. This state is determined by a bell state measuring circuit 15 using a linear optical element.
【００２３】図３において、図２の場合と同様に、第１
の２光子吸収結晶１１がΦ（＋）の２光子を吸収し、第
２の２光子吸収結晶１２がΦ（−）の２光子を吸収する
ようにして、減速子１３、１４を省略しても良い。In FIG. 3, as in the case of FIG.
The two-photon absorption crystal 11 absorbs two photons of Φ (+), the second two-photon absorption crystal 12 absorbs two photons of Φ (-), and the speed reducers 13 and 14 are omitted. Is also good.
【００２４】以上の回路ではΨ（±）状態を線形光学素
子によるベル状態測定回路１５で判別したが、減速子と
旋回子を用いてベル状態を変換し、４つの状態全てを２
光子吸収結晶で検出してもよい。例として、Γ１対称性
を持つ状態を２光子吸収の終状態とする結晶を用いた時
の量子回路の構成図を図４に示す。第２の２光子吸収結
晶１２を透過した光の一方の光路に偏光を９０度回転す
る旋回子３１を挿入する。この状態を第３の２光子吸収
結晶４１に入射するとΦ（＋）状態に変換されたΨ
（＋）状態だけが２光子吸収される。第３の２光子吸収
結晶を透過した光はｘおよびｙ方向を主軸として二つの
主軸方向の振動に９０度の位相差を与える減速子４３、
４４を通る。さらに、第４の２光子吸収結晶４２に入射
する。減速子によってΦ（−）状態に変換されていたΨ
（−）状態はさらにΦ（＋）状態に変換されるので第４
の２光子吸収結晶４２で２光子吸収される。以上、四つ
の２光子吸収結晶１１、１２、４１、４２により、おの
おの異なるベル状態が検出される。終状態が異なる対称
性を持つ場合でも同様にしてベル状態の検出が可能であ
る。In the above circuit, the Ψ (±) state is determined by the bell state measuring circuit 15 using a linear optical element. However, the bell state is converted by using a decelerator and a swivel, and all four states are converted into 2 states.
You may detect with a photon absorption crystal. As an example, FIG. 4 shows a configuration diagram of a quantum circuit using a crystal in which a state having Γ1 symmetry is a final state of two-photon absorption. A swirler 31 for rotating the polarization by 90 degrees is inserted into one optical path of the light transmitted through the second two-photon absorption crystal 12. When this state is incident on the third two-photon absorption crystal 41, it is converted into a Φ (+) state.
Only the (+) state is two-photon absorbed. The light transmitted through the third two-photon absorption crystal has a moderator 43 that gives a phase difference of 90 degrees to the vibrations in the two principal axes with the principal axes in the x and y directions.
Go through 44. Further, the light enters the fourth two-photon absorption crystal 42.減速 (-) state was converted by the decelerator.
Since the (-) state is further converted to the Φ (+) state,
Is absorbed by the two-photon absorption crystal. As described above, different bell states are detected by the four two-photon absorption crystals 11, 12, 41, and 42, respectively. Even when the final states have different symmetries, the bell state can be detected in the same manner.
【００２５】図４において、枠１０４、１０５で示す部
分は、図１の枠１０１で示す部分と同一であるが、これ
を図２の枠１０２で示す部分や図３の枠１０３で示す部
分に置き換えても良い。また、図３の枠１０３で示す部
分に置き換える場合に置いても、図３の量子回路を上述
のように変更できるのと同様に、第１の２光子吸収結晶
１１がΦ（＋）の２光子を吸収し、第２の２光子吸収結
晶１２がΦ（−）の２光子を吸収するようにして、減速
子１３、１４を省略しても良い。 以上の説明では結晶
を立方晶としたが、ｃ軸に入射光の方向がほぼ平行な場
合には六方晶や正方晶でも同様の選択則が成り立つので
本発明の量子回路に利用できる。例えば、ＺｎＯ， Ｚ
ｎＳｅ， ＣｄＳなどのＩＩ−ＶＩ族化合物が考えられ
る。量子井戸や量子箱のように電子の閉じ込め構造があ
る場合でも対称性を保っていれば用いることができる。
ポリフィリンなどの有機化合物も用いることができる。In FIG. 4, the portions indicated by frames 104 and 105 are the same as the portions indicated by frame 101 in FIG. 1, but are replaced by the portions indicated by frame 102 in FIG. 2 and the portions indicated by frame 103 in FIG. It may be replaced. In addition, even when the quantum circuit of FIG. 3 is replaced with the portion shown by the frame 103 in FIG. 3, the first two-photon absorption crystal 11 is replaced with the two of Φ (+) in the same manner as the quantum circuit of FIG. The moderators 13 and 14 may be omitted by absorbing the photons so that the second two-photon absorption crystal 12 absorbs the two-photons of Φ (-). In the above description, the crystal is a cubic crystal. However, when the direction of incident light is substantially parallel to the c-axis, the same selection rule holds for a hexagonal crystal and a tetragonal crystal, so that the crystal can be used in the quantum circuit of the present invention. For example, ZnO, Z
Group II-VI compounds such as nSe and CdS are contemplated. Even if there is an electron confinement structure such as a quantum well or a quantum box, it can be used if symmetry is maintained.
Organic compounds such as porphyrin can also be used.
【００２６】光を狭い領域に閉じ込めて電界強度を高め
る構造の中に２光子吸収結晶を挿入することで２光子吸
収確率を格段に高めることができる。このような構造の
例として図６に示すような２種類の半導体または誘電体
を交互に積層した多層膜反射鏡６１、６２に１波長の厚
さの２光子吸収結晶を含む層６３が挟まれているいわゆ
るファブリ・ペロ共振器構造がある。光は反射鏡にほぼ
垂直に入射する。２本の透過した光線を分離するため入
射角は０度より大きくなければならない。このような共
振器で光は１０μｍ3程度に閉じ込められる。また、光
子の寿命は１０ｐｓ程度になる。ベル状態にある２個の
光子が共振器内で作る電界の強度は１０ 4Ｖ／ｍ程度に
なる。ただし、２光子吸収結晶を含む層の屈折率は３程
度とした。２光子吸収結晶としてＣｕＣｌを用いると励
起子分子の巨大２光子吸収のため、２光子吸収係数は
０．１ｃｍ／Ｗと大きな値を持つ。共振器内で２光子吸
収される速度は０．１ｐｓ-1となり、光子寿命の間に２
光子吸収が１回起きることになり、ベル状態の検出がで
きる。Light is confined in a narrow area to increase the electric field strength.
Inserting a two-photon absorption crystal into a two-photon absorption crystal
The yield probability can be significantly increased. Of such a structure
For example, two types of semiconductors or dielectrics as shown in FIG.
Are alternately stacked on the multilayer mirrors 61 and 62 to a thickness of one wavelength.
Layer 63 containing a two-photon absorption crystal
Fabry-Perot resonator structure. Light is almost reflected
Incident vertically. Enter to separate the two transmitted rays
The firing angle must be greater than 0 degrees. Such sharing
Light is 10μm with a shakerThreeConfined to a degree. Also light
The life of the child is about 10 ps. Two bells
The intensity of the electric field created by photons in the resonator is 10 FourAbout V / m
Become. However, the refractive index of the layer containing the two-photon absorption crystal is about three
Degree. Use of CuCl as a two-photon absorption crystal encourages
Due to the giant two-photon absorption of the initiator molecule, the two-photon absorption coefficient is
It has a large value of 0.1 cm / W. Two-photon absorption in the cavity
Acquisition speed is 0.1ps-1And 2 during the photon lifetime
One photon absorption occurs, and the bell state is detected.
Wear.
【００２７】共振器の構造としてはファブリ・ペロ共振
器に限らず異なった誘電率を持つ２つ以上の物質を光の
波長程度の周期で交互に配列して構成されるフォトニッ
ク結晶の１部で周期性を乱すことによって作られた欠陥
部分を用いることもできる。このフォトニック結晶によ
る共振器はファブリ・ペロ共振器より小さな体積に光を
閉じ込めることができ、光子寿命も長くできるのでベル
状態を検出する確率をさらに増大できる。The structure of the resonator is not limited to the Fabry-Perot resonator, and is a part of a photonic crystal formed by alternately arranging two or more substances having different dielectric constants at a cycle of about the wavelength of light. A defective portion formed by disturbing the periodicity can be used. The photonic crystal resonator can confine light in a smaller volume than the Fabry-Perot resonator, and can extend the photon lifetime, so that the probability of detecting the bell state can be further increased.
【００２８】また、共振器を用いず、導波路によって光
の電界強度を高めることもできる。もちろん、２光子吸
収結晶の２光子吸収係数が十分大きければ光を閉じ込め
るための構造は必要ではない。Further, the electric field intensity of light can be increased by a waveguide without using a resonator. Of course, if the two-photon absorption coefficient of the two-photon absorption crystal is sufficiently large, a structure for confining light is not necessary.
【００２９】[0029]
【発明の効果】以上説明したように、本発明によれば、
結晶の対称性により特定の偏光方向をもつ２光子の組を
吸収する２光子吸収結晶と、２光子吸収結晶における２
光子吸収を検出する手段と、偏光の状態を変換する偏光
要素という基本構成に基づき、他の電磁場による原子状
態の準備が不要な材料を用いてベル状態測定を実現した
実用的な量子回路が提供される。本発明では気体ではな
く結晶を用いているため２光子吸収強度が大きく、十分
高い確率ベル状態の検出が実現される。また、四つのベ
ル状態を個別に検出しているので検出の失敗による誤り
は小さく抑えられる。As described above, according to the present invention,
A two-photon absorption crystal that absorbs a set of two-photons having a specific polarization direction due to the symmetry of the crystal;
Based on the basic configuration of a means for detecting photon absorption and a polarizing element that converts the state of polarization, a practical quantum circuit that achieves Bell state measurement using materials that do not require preparation of atomic states by other electromagnetic fields is provided Is done. In the present invention, since a crystal is used instead of a gas, the two-photon absorption intensity is large, and a sufficiently high probability bell state can be detected. Further, since the four bell states are individually detected, errors due to detection failure can be reduced.
【００３０】なお、本発明は上記各実施例に限定され
ず、本発明の技術思想の範囲内において、各実施例は適
宜変更され得ることは明らかである。It should be noted that the present invention is not limited to the above embodiments, and it is clear that each embodiment can be appropriately modified within the scope of the technical idea of the present invention.
【図１】本発明の一実施例を示す量子回路の構成図。FIG. 1 is a configuration diagram of a quantum circuit showing one embodiment of the present invention.
【図２】本発明の別の実施例を示す量子回路の構成図。FIG. 2 is a configuration diagram of a quantum circuit showing another embodiment of the present invention.
【図３】本発明のもう一つの実施例を示す量子回路の構
成図。FIG. 3 is a configuration diagram of a quantum circuit showing another embodiment of the present invention.
【図４】本発明の別の実施の形態を示す量子回路の構成
図。FIG. 4 is a configuration diagram of a quantum circuit showing another embodiment of the present invention.
【図５】線形光学素子によるベル状態測定回路の構成
図。FIG. 5 is a configuration diagram of a bell state measuring circuit using a linear optical element.
【図６】２光子吸収結晶を挿入する共振器の一例の構造
図。FIG. 6 is a structural diagram of an example of a resonator into which a two-photon absorption crystal is inserted.
１１ 第１の２光子吸収結晶 １２ 第２の２光子吸収結晶 １３ 減速子 １４ 減速子 １５ 線形光学素子によるベル状態測定回路 １６ 光伝導検出器 １７ 光伝導検出器 ２１ 電源 ２２ 電源 ３１ 旋回子 ３２ 旋回子 ４１ 第３の２光子吸収結晶 ４２ 第４の２光子吸収結晶 ４３ 減速子 ４４ 減速子 ４５ 光伝導検出器 ４６ 光伝導検出器 ５１ 半透鏡 ５２ 偏光ビームスプリッタ ５３ 偏光ビームスプリッタ ５４ 光子検出器 ５５ 光子検出器 ５６ 光子検出器 ５７ 光子検出器 ６１ 多層膜反射鏡 ６２ 多層膜反射鏡 ６３ ２光子吸収結晶を含む層 DESCRIPTION OF SYMBOLS 11 1st two-photon absorption crystal 12 2nd two-photon absorption crystal 13 Speed reducer 14 Speed reducer 15 Bell state measuring circuit by linear optical element 16 Photoconductive detector 17 Photoconductive detector 21 Power supply 22 Power supply 31 Swirler 32 Turning Element 41 Third two-photon absorption crystal 42 Fourth two-photon absorption crystal 43 Moderator 44 Moderator 45 Photoconductive detector 46 Photoconductive detector 51 Semi-transparent mirror 52 Polarized beam splitter 53 Polarized beam splitter 54 Photon detector 55 Photon Detector 56 photon detector 57 photon detector 61 multilayer reflector 62 multilayer reflector 63 layer containing two-photon absorption crystal
───────────────────────────────────────────────────── フロントページの続き (51)Int.Cl.7 識別記号 ＦＩ テーマコート゛(参考） Ｈ０４Ｂ 10/00 Ｈ０４Ｂ 9/00 Ｚ ──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. 7 Identification symbol FI Theme coat ゛ (Reference) H04B 10/00 H04B 9/00 Z
Claims (18)
において、偏光が相互に定まった関係にある２光子の組
を吸収する２光子吸収結晶と、前記２光子吸収結晶での
２光子の吸収を検出する２光子吸収検出器と、前記２光
子吸収結晶を通過した光子の偏光状態を変換する偏光要
素と、を備えることを特徴とする量子回路。In a quantum optical circuit for detecting a quantum state of an optical signal, a two-photon absorption crystal that absorbs a set of two photons whose polarizations are mutually defined, and a two-photon absorption crystal of the two-photon absorption crystal. A quantum circuit comprising: a two-photon absorption detector for detecting absorption; and a polarization element for converting a polarization state of a photon that has passed through the two-photon absorption crystal.
ベル状態であることを特徴とする請求項１に記載の量子
回路。2. The quantum circuit according to claim 1, wherein the quantum states are four kinds of bell states represented by polarized light.
共振器の中に設けられたことを特徴とする請求項１又は
２に記載の量子回路。3. The quantum circuit according to claim 1, wherein the two-photon absorption crystal is provided in a resonator that resonates with incident light.
（＋）、Φ（−）、Ψ（＋）及びΨ（−）のうちのいず
れの状態にあるかを検出する量子回路において、 ２光子を入射し、状態Φ（＋）及び状態Φ（−）のうち
の第１の状態の２光子を吸収する第１の２光子吸収結晶
と、 前記第１の２光子吸収結晶での２光子の吸収を検出する
第１の検出器と、 前記第１の２光子吸収結晶を通過した２光子を入射し、
状態Ψ（＋）又は状態Ψ（−）を検出する線形光学素子
と光子検出器から成る検出回路と、 を備えることを特徴とする量子回路。4. The incident two photons have four bell states Φ.
In a quantum circuit for detecting which of (+), Φ (-), Ψ (+), and Ψ (-), two photons are incident, and a state Φ (+) and a state Φ (- ), A first two-photon absorption crystal that absorbs two photons in a first state, a first detector that detects two-photon absorption in the first two-photon absorption crystal, Incident on the two-photon absorption crystal passing through the two-photon absorption crystal,
A quantum circuit comprising: a linear optical element that detects a state Ψ (+) or a state Ψ (−); and a detection circuit including a photon detector.
記第１の２光子吸収結晶と前記検出回路の間に、 前記第１の２光子吸収結晶を通過した２光子を入射し、
入射した２光子の状態Φ（＋）及び状態Φ（−）のうち
の第２の状態を前記第１の状態に変換する偏光要素と、 前記偏光要素を通過した２光子を入射し、前記第１の状
態の２光子を吸収する第２の２光子吸収結晶と、 前記第２の２光子吸収結晶での２光子の吸収を検出する
第２の検出器と、 を備えることを特徴とする量子回路。5. The quantum circuit according to claim 4, wherein two photons passing through the first two-photon absorption crystal are incident between the first two-photon absorption crystal and the detection circuit;
A polarizing element that converts a second state of the incident two-photon state Φ (+) and state Φ (−) into the first state; and a two-photon that has passed through the polarizing element. A second two-photon absorption crystal that absorbs the two-photon in the first state; and a second detector that detects two-photon absorption in the second two-photon absorption crystal. circuit.
記第１の２光子吸収結晶と前記検出回路の間に、 前記第１の２光子吸収結晶を通過した２光子を入射し、
入射した２光子の状態Φ（＋）及び状態Φ（−）のうち
の第２の状態の２光子を吸収する２光子吸収結晶と、 前記第２の２光子吸収結晶での２光子の吸収を検出する
第２の検出器と、 を備えることを特徴とする量子回路。6. The quantum circuit according to claim 4, wherein two photons passing through the first two-photon absorption crystal are incident between the first two-photon absorption crystal and the detection circuit;
A two-photon absorption crystal that absorbs a two-photon in a second state of the incident two-photon state Φ (+) and state Φ (-); and a two-photon absorption crystal in the second two-photon absorption crystal. A quantum circuit comprising: a second detector for detecting.
量子回路において、 前記第１の２光子吸収結晶の入射側に、自らが入射した
２光子の状態Φ（±）を状態Ψ（±）に、状態Ψ（±）
を状態Φ（±）に変換する第１の偏光素子を、 前記第２の２光子吸収結晶の出射側に、自らが入射した
２光子の状態Φ（±）を状態Ψ（±）に、状態Ψ（±）
を状態Φ（±）に変換する第２の偏光素子を、 更に備えることを特徴とする量子回路。7. The quantum circuit according to claim 4, wherein a state Φ (±) of a two-photon incident on the incident side of the first two-photon absorption crystal is represented by a state Ψ. (±), state Ψ (±)
Is converted into a state Φ (±) by changing the state Φ (±) of the two-photon incident on itself to the state Ψ (±) on the emission side of the second two-photon absorption crystal. Ψ (±)
A quantum circuit, further comprising: a second polarizing element that converts the state into a state Φ (±).
共振器の中に設けられたことを特徴とする請求項４乃至
７のいずれか１項に記載の量子回路。8. The quantum circuit according to claim 4, wherein the two-photon absorption crystal is provided in a resonator that resonates with incident light.
（＋）、Φ（−）、Ψ（＋）及びΨ（−）のうちのいず
れの状態にあるかを検出する量子回路において、 ２光子を入射し、状態Φ（＋）又は状態Φ（−）の２光
子を検出する第１の検出部と、 前記第１の検出部を通過した２光子を入射し、入射した
２光子の状態Φ（±）を状態Ψ（±）に、状態Ψ（±）
を状態Φ（±）に変換する第１の偏光素子と、 前記第１の偏光素子を通過した２光子を入射し、状態Φ
（＋）又は状態Φ（−）の２光子を検出する第２の検出
部と、 を備えることを特徴とする量子回路。9. The incident two photons have four bell states Φ
In a quantum circuit for detecting which of (+), Φ (-), Ψ (+), and Ψ (-), two photons are incident, and a state Φ (+) or a state Φ (- ), A first detector for detecting two photons, and two photons passing through the first detector are incident, and the state Φ (±) of the incident two photons is changed to a state Ψ (±), and a state Ψ ( ±)
Into a state Φ (±), and a two-photon that has passed through the first polarizing element is incident, and a state Φ
And a second detector for detecting two photons in (+) or state Φ (-).
の第１の状態の２光子を吸収する第１の２光子吸収結晶
と、 前記第１の２光子吸収結晶での２光子の吸収を検出する
第１の検出器と、 前記第１の２光子吸収結晶を通過した２光子を入射し、
状態Ψ（＋）又は状態Ψ（−）を検出する線形光学素子
と光子検出器から成る検出回路と、 を備えることを特徴とする量子回路。10. The quantum circuit according to claim 9, wherein the first detector receives two photons, and two photons in a first state of the state Φ (+) and the state Φ (−). A first two-photon absorption crystal that absorbs light; a first detector that detects the absorption of two photons in the first two-photon absorption crystal; and a two-photon that has passed through the first two-photon absorption crystal. Incident,
A quantum circuit comprising: a linear optical element that detects a state Ψ (+) or a state Ψ (−); and a detection circuit including a photon detector.
て、前記第１の２光子吸収結晶と前記検出回路の間に、 前記第１の２光子吸収結晶を通過した２光子を入射し、
入射した２光子の状態Φ（＋）及び状態Φ（−）のうち
の第２の状態を前記第１の状態に変換する偏光要素と、 前記偏光要素を通過した２光子を入射し、前記第１の状
態の２光子を吸収する第２の２光子吸収結晶と、 前記第２の２光子吸収結晶での２光子の吸収を検出する
第２の検出器と、 を備えることを特徴とする量子回路。11. The quantum circuit according to claim 10, wherein two photons passing through the first two-photon absorption crystal are incident between the first two-photon absorption crystal and the detection circuit;
A polarizing element that converts a second state of the incident two-photon state Φ (+) and state Φ (−) into the first state; and a two-photon that has passed through the polarizing element. A second two-photon absorption crystal that absorbs the two-photon in the first state; and a second detector that detects two-photon absorption in the second two-photon absorption crystal. circuit.
て、前記第１の２光子吸収結晶と前記検出回路の間に、 前記第１の２光子吸収結晶を通過した２光子を入射し、
入射した２光子の状態Φ（＋）及び状態Φ（−）のうち
の第２の状態の２光子を吸収する２光子吸収結晶と、 前記第２の２光子吸収結晶での２光子の吸収を検出する
第２の検出器と、 を備えることを特徴とする量子回路。12. The quantum circuit according to claim 10, wherein two photons passing through the first two-photon absorption crystal are input between the first two-photon absorption crystal and the detection circuit,
A two-photon absorption crystal that absorbs a two-photon in a second state of the incident two-photon state Φ (+) and state Φ (-); and a two-photon absorption crystal in the second two-photon absorption crystal. A quantum circuit comprising: a second detector for detecting.
記載の量子回路において、 前記第１の２光子吸収結晶の入射側に、自らが入射した
２光子の状態Φ（±）を状態Ψ（±）に、状態Ψ（±）
を状態Φ（±）に変換する第１の偏光素子を、 前記第２の２光子吸収結晶の出射側に、自らが入射した
２光子の状態Φ（±）を状態Ψ（±）に、状態Ψ（±）
を状態Φ（±）に変換する第２の偏光素子を、 更に備えることを特徴とする量子回路。13. The quantum circuit according to claim 10, wherein a state Φ (±) of a two-photon incident on the incident side of the first two-photon absorption crystal is represented by a state Ψ. (±), state Ψ (±)
Is converted into a state Φ (±) by changing the state Φ (±) of the two-photon incident on itself to the state Ψ (±) on the emission side of the second two-photon absorption crystal. Ψ (±)
A quantum circuit, further comprising: a second polarizing element that converts the state into a state Φ (±).
の第１の状態の２光子を吸収する第１の２光子吸収結晶
と、 前記第１の２光子吸収結晶での２光子の吸収を検出する
第１の検出器と、 前記第１の２光子吸収結晶を通過した２光子を入射し、
状態Ψ（＋）又は状態Ψ（−）を検出する線形光学素子
と光子検出器から成る検出回路と、 を備えることを特徴とする量子回路。14. The quantum circuit according to claim 9, wherein the second detector receives two photons, and has two photons in a first state of the state Φ (+) and the state Φ (−). A first two-photon absorption crystal that absorbs light; a first detector that detects the absorption of two photons in the first two-photon absorption crystal; and a two-photon that has passed through the first two-photon absorption crystal. Incident,
A quantum circuit comprising: a linear optical element that detects a state Ψ (+) or a state Ψ (−); and a detection circuit including a photon detector.
て、前記第１の２光子吸収結晶と前記検出回路の間に、 前記第１の２光子吸収結晶を通過した２光子を入射し、
入射した２光子の状態Φ（＋）及び状態Φ（−）のうち
の第２の状態を前記第１の状態に変換する偏光要素と、 前記偏光要素を通過した２光子を入射し、前記第１の状
態の２光子を吸収する第２の２光子吸収結晶と、 前記第２の２光子吸収結晶での２光子の吸収を検出する
第２の検出器と、 を備えることを特徴とする量子回路。15. The quantum circuit according to claim 14, wherein two photons passing through the first two-photon absorption crystal are incident between the first two-photon absorption crystal and the detection circuit,
A polarizing element that converts a second state of the incident two-photon state Φ (+) and state Φ (−) into the first state; and a two-photon that has passed through the polarizing element. A second two-photon absorption crystal that absorbs the two-photon in the first state; and a second detector that detects two-photon absorption in the second two-photon absorption crystal. circuit.
て、前記第１の２光子吸収結晶と前記検出回路の間に、 前記第１の２光子吸収結晶を通過した２光子を入射し、
入射した２光子の状態Φ（＋）及び状態Φ（−）のうち
の第２の状態の２光子を吸収する２光子吸収結晶と、 前記第２の２光子吸収結晶での２光子の吸収を検出する
第２の検出器と、 を備えることを特徴とする量子回路。16. The quantum circuit according to claim 14, wherein two photons passing through the first two-photon absorption crystal are incident between the first two-photon absorption crystal and the detection circuit,
A two-photon absorption crystal that absorbs a two-photon in a second state of the incident two-photon state Φ (+) and state Φ (-); and a two-photon absorption crystal in the second two-photon absorption crystal. A quantum circuit comprising: a second detector for detecting.
記載の量子回路において、 前記第１の２光子吸収結晶の入射側に、自らが入射した
２光子の状態Φ（±）を状態Ψ（±）に、状態Ψ（±）
を状態Φ（±）に変換する第１の偏光素子を、 前記第２の２光子吸収結晶の出射側に、自らが入射した
２光子の状態Φ（±）を状態Ψ（±）に、状態Ψ（±）
を状態Φ（±）に変換する第２の偏光素子を、 更に備えることを特徴とする量子回路。17. The quantum circuit according to claim 14, wherein a state Φ (±) of the two-photon incident on the incident side of the first two-photon absorption crystal is represented by a state Ψ. (±), state Ψ (±)
Is converted into a state Φ (±) by changing the state Φ (±) of the two-photon incident on itself to the state Ψ (±) on the emission side of the second two-photon absorption crystal. Ψ (±)
A quantum circuit, further comprising: a second polarizing element that converts the state into a state Φ (±).
る共振器の中に設けられたことを特徴とする請求項１０
乃至１７のいずれか１項に記載の量子回路。18. The apparatus according to claim 10, wherein said two-photon absorption crystal is provided in a resonator that resonates with incident light.
18. The quantum circuit according to any one of claims 17 to 17.
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| US5233242A (en) * | 1991-08-14 | 1993-08-03 | Westinghouse Electric Corp. | Superconducting push-pull flux quantum gate array cells |
| US5264711A (en) * | 1992-09-15 | 1993-11-23 | The United States Of America As Represented By The Secretary Of The Army | Metal-encapsulated quantum wire for enhanced charge transport |
| US6321182B1 (en) * | 1995-03-27 | 2001-11-20 | Canon Kabushiki Kaisha | Method and system for predicting a signal generated in signal processing apparatus |
| US6057541A (en) * | 1997-03-18 | 2000-05-02 | Ansible, Inc. | Method and apparatus for selectively controlling the quantum state probability distribution of correlated quantum objects |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2007143085A (en) * | 2005-11-22 | 2007-06-07 | Hiroshima Univ | Quantum state transfer method |
| WO2009133877A1 (en) * | 2008-05-01 | 2009-11-05 | 公立大学法人大阪府立大学 | Photon pair generator and photon pair production method |
| US8441719B2 (en) | 2008-05-01 | 2013-05-14 | Osaka Prefecture University Public Corporation | Photon pair generating apparatus and photon pair generating method |
| JP5224417B2 (en) * | 2008-05-01 | 2013-07-03 | 公立大学法人大阪府立大学 | Photon pair generation apparatus and photon pair generation method |
Also Published As
| Publication number | Publication date |
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| JP3981969B2 (en) | 2007-09-26 |
| US20020030186A1 (en) | 2002-03-14 |
| US6444999B1 (en) | 2002-09-03 |
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